It has become the practice in many hydraulic, transmission, and engine lubricating systems, to provide a magnet whose function is to capture and retain magnetically attractable particles entrained in the fluid medium in the system, and thus protect the pumps, seals and other components of the system from abrasive damage or the like should such particles be allowed to freely circulate through the system. In some instances the magnet is associated with a filter cartridge or element which will filter out other undesirable contaminants and the combination thus provides a filter which will capture and remove both magnetically attractable and nonmagnetically attractable contaminants. In this type of filter the magnets have generally been of the following types:
A. ALNICO magnets, comprising a mixture of aluminum, nickel, and copper. These magnets are limited in size and shape that can be readily manufactured, and are somewhat brittle and costly.
B. Ferrite permanent magnets, which are formed as a ceramic artlcle such as a disc or the like, and which while less costly than the ALNICO magnets, must be cast and/or machined into the desired shape, and are quite brittle.
C. Ferrite particle magnets which comprise ferrite particles injection molded or extruded in a plastic vehicle body such as nylon, polyester, etc. While less brittle than the first two types, these magnets have a relatively low magnetic energy field and involve a high tooling cost.
D. Rubber bonded barium ferrite magnets, sold under the trademark PLASTIFORM, by 3 M Company, in which the barium ferrite particles are highly oriented during processing. These magnets, while possessing satisfactory magnetic strength, break down if exposed to hot hydraulic oils and other liquid media often encountered in systems in which it would be desirable to use the magnets, and the resulting pieces of the magnet can enter the fluid system as contaminants.
Brittleness of types A and B mentioned above imposes serious limitations not only on the mounting of the magnets to avoid fracture under vibration and fluid pressure forces, but in cleaning them for reuse great care must be taken to guard against inadvertent breakage. Breaking or chipping of these magnets while in use allows the detached pieces to foul the system and cause premature wear or failure of the system components. Because of the difficulty in cleaning these types of magnets it is often cheaper to replace them than to clean them.
The weakness of the magnetic field of type C mentioned above and the deterioration of type D has militated against their use. If type D deteriorates or delaminates, deleterious particles can enter the fluid system leading to early wear or failure of the system components.
However, the type D magnet mentioned above, because of its low cost, ductility or flexibility, high magnetic field strength, and ease with which it may be shaped, would be a highly desirable type of magnet to use if the problem of deterioration and delamination in the presence of the liquid to be filtered could be inexpensively solved while not adversely affecting its field strength, and at the same time the magnet rigidified somewhat so that it could become part of a structural filter assembly.